Passive infrared (PIR) sensors or passive infrared detectors (PIDs) are generally known. Such devices find ready use as intrusion detectors in security systems.
A PID device detects intrusion via the infrared radiation emitted by humans. However, PID devices suffer from the difficulty of not being able to differentiate between humans and animals and in not being able to detect humans against hot background surfaces.
One particular type of PID devices is a PID motion detector. A PID motion detector uses a pair of infrared detectors arranged to scan adjacent areas. In this regard, the pair of detectors may be connected in series so that when both areas have the same background temperature, the signal from the one will cancel the signal from the other.
PID motion detectors have been found to be considerably more reliable than when PID devices are used individually and especially when combined and used with a microwave motion detector. Since the PIDs are connected to cancel one another, PID motion detectors are less vulnerable to transients, e.g., flashes of light (e.g., lightning) detected by the pair of detectors. When combined with a microwave transceiver the two devices can be logically ANDed to provide an even more reliable device.
While a combined PID motion detector and microwave motion detector is a significant improvement, it is bulky and expensive. Accordingly, a need exists for improved motion detection devices.